1. Field of the Invention
This invention relates to grinding mills, and specifically relates to a mill liner and mill liner assembly for grinding mills.
2. Description of the Related Art
Grinding mills are used in various industries to process hard, solid materials, such as rock and mineral ores, to crush, grind or comminute the material into smaller sizes. Grinding mills can vary in their structural configuration and materials of construction, and in the manner used to crush the solids.
Grinding mills to which the present disclosure is generally directed are comprised of a rotatable drum, also referred to as a shell, having a cylindrical wall and two open ends. In use, material flows in one end and out the other end of the drum. The axis of the drum is most typically horizontal or angled in orientation during operation. The interior of the drum or shell forms a treatment chamber into which the material to be processed is fed. Solid material is fed into the drum, sometimes along with steel balls which are used for aiding the grinding process (e.g., SAG mills), and the drum is rotated. In some processing operations, grinding rods are used instead of steel balls, but the grinding rods are added into the mill separately from the feed.
As the drum rotates, the solid material is lifted up along the inside wall of the drum until the material reaches a point where gravity causes the solid material to fall downwardly to the lowest point of the drum. By this operation, the solid material, along with the steel balls or rods when used, produce a crushing and grinding of the material.
The grinding mill drum or shell is lined with various elements that protect the inner wall of the shell and which are especially designed and positioned within the drum to provide optimal crushing or grinding of the solids. The particular liner elements employed in a grinding mill are specifically determined by and selected in light of the type of solids being processed and the type of crushing or size of crushed material that is desired, as well as other factors such as the size of the mill and the size of the particulate material being fed into the mill.
Liner elements may conventionally include liner plates and lifter bars which are positioned along the inner wall of the drum or shell. Lifter bars assist in lifting the charge (i.e., the solid material being processed) up the side of the shell as the shell rotates. Liner plates, also known and referred to as shell plates or spacers, are used to line the inner wall of the shell, in between the lifter bars, and protect the inner wall of the shell from damage due to abrasion and impact of solid material. The configuration and dimensions of liner plates and lifter bars are selected based on the material being crushed and the type or size of crushing or grinding that is desired.
The liner elements described are most conventionally made of steel or similar material that can withstand the impact of the solid material as it is processed in the rotating drum. Rubber or elastomers have also been used in some liner elements. For example, a mill liner assembly comprising a wear element for positioning between lifter bars in a grinding mill drum is described in U.S. Published Application No. 2008/0265074 A1. The wear element described in that application includes a cushioning plate made partially of elastomeric material that absorbs the impact of the solids material, thereby protecting the shell.
As is well-known in the art of grinding mills, the components of the mill liner eventually crack and/or wear away over time due to the continuous impact of solids against the elements, and replacement of the elements is required. This necessitates that the mill be stopped for a period of time, which causes the cessation of the grinding of material, and may also necessitate the shutting down of other machinery in a plant that operates to further process the material produced by the mill.
In conventional grinding mill configurations that employ steel mill liner components, the process required for replacing broken steel elements is costly, not only because of the operating downtime necessary to replace the broken elements, but also because of the cost of the liner elements. The significant weight of the steel components often requires heavy equipment to move the steel components making repair or replacement difficult and costly. Additionally, broken steel liner elements present dangerous conditions for workers and technicians since the broken pieces of the liner elements are loose and may fall from the wall of the shell endangering human life. The steel liners also present a considerable impact on transport and repair costs due to the weight of the liners.
While the use of elastomer in mill liner elements has resulted in reduced weight of those structures for transport and handling purposes, elastomer liner elements present other limitations, including construction and configuration limitations, and limitations on service life of the liner elements. Additionally, the use of elastomer liner elements in grinding mills has led to the use of lifter bars as a means for anchoring the individual liner plates that are interspaced between the lifter bars about the inner circumference of the rotating drum, a factor which presents additional construction costs in terms of transportation of parts and increased assembly requirements.
It has heretofore been impossible to effectively simplify the assembly and replacement or repair of grinding mills liner elements. Thus, it would be beneficial to overcome the foregoing problems experienced with conventional mill liner assemblies by providing mill liner elements that are more easily handled, more easily installed and replaced, and that result in less operational downtime when being replaced.